In many cases in microsystems technology, electronic, electromechanical or purely mechanical microcomponents are glued to a substrate. The precision which is needed here, the low bond areas, and the need to automate the joining operation pose a particular problem here. Microcomponents are conventionally glued using viscous adhesives as one- or two-part systems which have a specific potlife within which the adhesion properties are retained and the bonding operation can be implemented. Viscous adhesives, moreover, have a specific cure time which the adhesive needs in order to ensure a stable bond.
Publications U.S. Pat. No. 6,126,765, US 2003/0029724 A1, and WO 98/45693 describe methods of this kind for bonding microstructures using viscous hotmelt adhesives.
The potlife ought to be as long as possible, in order to allow rational joining of microcomponents by extensive application of the adhesive to the substrate, and subsequent joining of a multiplicity of microcomponents to the substrate in a time required for the operation. On the other hand, the pot life and cure time should be as short as possible, so that the adhesive bond cures immediately after the joining operation and the microcomponents are not displaced on the substrate. These two contrary boundary conditions are almost impossible to reconcile with one another. A further complicating factor is the low thickness of the film of adhesive that is required in microsystems technology, in the μm range, which is different from macroscopic bonding.
DE 198 50 041 A1 describes a microtechnological bonding method of producing an adhesive bond using a liquid or pasty hotmelt adhesive which has at least a viscosity such that it can be placed as a string of adhesive with a defined cross section on one of the adherends. The gluing effect is only developed under specific external conditions—heating of the adhesive, for example—so that the string of adhesive can be displaced, owing to the as yet absent or minimal adhesion tendency. However, this may result in the desired bond area being only partly wetted with the required amount of adhesive, which leads to a significant reduction in the quality of the joint.
DE 37 39 333 A1 describes a method of producing hotmelt adhesive bonds that uses a laser as its heat source. The method envisages treating the reverse face of the adherend wafers by coating them with a hotmelt adhesive solution or with an adhesive varnish in a varnish spin-coating unit or laminating them by means of an adhesive sheet, using a sheet ironing unit. The wafers are subsequently sawn in the usual way, and the individualized chips are dried. The chips are then lifted cyclically and simultaneously from the wafer and fixed in pairs using the laser. The energy of the laser beam serves here to melt the adhesive in order to produce the joining of the adherends.